Heat-stable hydrated salt long-term phase change heat storage composite material capable of adjusting phase change temperature and preparation method of heat-stable hydrated salt long-term phase change heat storage composite material

Abstract

The invention discloses a heat-stable heat-storage phase-change composite material capable of adjusting the phase-change temperature and a preparation method thereof, and belongs to the technical field of phase-change materials. The composite material comprises the following components in percentage by weight: 60-80% of hydrated salt, 5-20% of polyol, 10-20% of a primary packaging material, 3-8% of a secondary packaging material and 1-5% of a heat conduction reinforcing material. The preparation method mainly comprises the following steps: melting hydrated salt, and mixing the molten hydrated salt with polyol to form a uniform precursor; carrying out primary packaging, adsorption and shaping by utilizing a porous material; carrying out secondary coating and curing through a polymer solution; and finally carrying out vacuum drying treatment. The core of the invention lies in that a hydrogen bond network is constructed by polyol to accurately regulate and control the phase change temperature and inhibit phase separation, and the problems of fixed phase change temperature, easy leakage, poor cycle stability, poor thermal conductivity and the like of a traditional hydrated salt material are cooperatively solved by combining primary packaging of a porous carrier and secondary sealing of a polymer layer.

Description

Technical Field

[0001] This invention relates to the field of phase change materials, specifically to a thermally stable thermal storage phase change composite material with adjustable phase change temperature and its preparation method. Background Technology

[0002] With the continuous expansion of renewable energy utilization, the imbalance between energy supply and demand in both time and space is becoming increasingly prominent. Developing efficient and stable thermal storage technologies has become crucial for achieving intertemporal thermal control of energy. Phase change thermal storage technology has attracted widespread attention due to its high energy density and near-isothermal heat storage and release processes. Among various phase change materials, inorganic hydrated salts (such as sodium acetate trihydrate, SAT) have shown promising application prospects in building energy conservation, solar thermal storage, and industrial waste heat recovery due to their advantages such as large latent heat of phase change, high thermal conductivity, low raw material cost, and non-flammability. However, hydrated salt phase change materials, especially SAT, have long been limited by some inherent technical challenges in practical applications: First, during repeated melt-crystallization cycles, hydrated salts are prone to phase separation, i.e., the separation of crystal water and metal salt, leading to a significant decrease in thermal storage performance. Second, hydrated salts are prone to leakage in the molten state, and their phase change temperature is relatively fixed, making it difficult to flexibly adapt to the temperature requirements of different application scenarios. For example, the phase change temperature of SAT is approximately 58°C, limiting its application in areas requiring other operating temperature ranges.

[0003] To address these challenges, traditional improvement methods mainly include adding thickeners or altering viscosity with other components. Adding carboxymethyl cellulose can suppress phase separation to some extent, but excessive addition significantly reduces the material's thermal conductivity and heat storage density. Introducing substances like urea to form a eutectic system with SAT can regulate the phase transition temperature, but may introduce new problems such as slow exothermic rates and intensified phase separation. Furthermore, using porous materials for adsorption and encapsulation of hydrated salts is an effective way to solve leakage and improve shape stability. These porous carriers can adsorb hydrated salts due to their abundant pore structure and surface properties, and their surface hydrophilic groups help improve compatibility. However, research shows that relying solely on porous materials for adsorption and encapsulation has limitations: the open channels inside the porous material and the "climbing" phenomenon of hydrated salts outside the channels mean that the adsorbed hydrated salts may still come into contact with the external environment, causing the water of crystallization to gradually escape during long-term circulation, and the thermal reliability problem remains unresolved. Some studies have attempted to re-encapsulate hydrated salt-porous material composite systems using secondary coating techniques such as in-situ polymer polymerization or adsorption coating. However, these methods may have drawbacks such as complex processes, the need for large amounts of solvents, easy cracking of the coating layer, difficulty in continuously and effectively blocking the open channels of porous materials, and potential reduction in the overall thermal conductivity of the material.

[0004] To address the aforementioned issues, this invention proposes a spatiotemporal phase change thermal energy storage composite system with adjustable phase change temperature achieved through the combination of polyols and hydrated salts. The polyols can form a stable hydrogen bond network with water molecules in the hydrated salt system, allowing for controllable adjustment of the phase change temperature by regulating the polyol ratio. Simultaneously, the high viscosity of the polyols effectively suppresses phase separation and water migration, improving the cycle stability and thermal response reversibility of the composite system while maintaining stable supercooling characteristics of the SAT (Standard Availability Temperature). A secondary encapsulation strategy is employed, first adsorbing the hydrated salt onto a porous carrier, then surface-coating it with liquid fluororubber or acrylic emulsion, enhancing thermal stability while preventing leakage. This composite system enables continuous adjustment of the phase change temperature and spatiotemporal stable control of the thermal storage process, providing a new solution for the practical application of hydrated salt phase change energy storage materials. Summary of the Invention

[0005] This invention addresses the problems of severe phase separation, single phase change temperature, leakage, and poor stability associated with sodium acetate trihydrate as a phase change thermal storage material. It proposes a thermally stable phase change thermal storage composite material with adjustable phase change temperature, modified by polyol blending and secondary encapsulation, and its preparation method.

[0006] The technical solution of the present invention is as follows: the material uses sodium acetate trihydrate as the matrix, and introduces polyols to regulate the phase change temperature and thicken and slow down phase separation. In addition, it uses a porous network structure to improve thermal conductivity and adsorb liquid phase change materials to achieve one-time encapsulation. Then, it forms a flexible sealing layer by polymer coating, thereby achieving high heat storage density, long-term subcooling stability and long cycle life.

[0007] A thermally stable phase change composite material with adjustable phase change temperature, wherein the weight percentage of each component is as follows: Hydrated salts: 60-80% Polyols: 5-20% Thermal conductivity enhancement material: 1-5% Primary encapsulation material: 10-20% Secondary encapsulation material: 3-8%; The primary encapsulation material is any one or more of expanded graphite, diatomaceous earth, expanded vermiculite, copper foam, nickel foam, and aluminum foam; the secondary encapsulation material is any one or more of acrylic emulsion, liquid fluororubber, epoxy resin, silicone, and high-temperature phase change wax.

[0008] Preferably, the hydrated salt is sodium acetate trihydrate.

[0009] Polyols, as phase transition temperature regulators, exhibit unique advantages in controlling the phase transition temperature of hydrated salts and slowing down phase separation. The polyols used are ethylene glycol, propylene glycol, glycerol, pentaerythritol, sorbitol, xylitol, erythritol, and mannitol. Most preferably, the polyol is erythritol.

[0010] The primary encapsulation material plays two main roles in phase change thermal storage composite materials: first, it adsorbs liquid phase change material through its porous structure, solving the leakage problem in its molten state and giving the material shape stability; second, it serves as a thermally conductive skeleton, improving the overall thermal conductivity of the composite material and accelerating the thermal storage and release process.

[0011] The function of secondary encapsulation materials in phase change thermal storage composite materials is to build a dense protective layer on the basis of primary encapsulation, aiming to completely solve the leakage problem and significantly improve the overall performance and service life of the material.

[0012] Preferably, the primary encapsulation material is expanded graphite.

[0013] Preferably, the secondary encapsulation material is an acrylic emulsion.

[0014] In phase change thermal storage composite materials, the core role of thermally conductive reinforcing materials is to significantly improve the thermal conductivity of the composite material, ensuring rapid and uniform heat transfer, thereby optimizing the efficiency of the heat storage and release processes. Preferably, the thermally conductive reinforcing materials are boron nitride, alumina, aluminum nitride, copper powder, aluminum powder, graphite sheets, and carbon nanotubes. Most preferably, the thermally conductive reinforcing material is graphite sheets.

[0015] This invention also provides a method for preparing a thermally stable phase change composite material with adjustable phase change temperature, comprising the following steps: Step 1: Heat the hydrated salt to melt it, then add the polyol while stirring and mix evenly to form a homogeneous liquid precursor; Step 2: Add primary encapsulation material and thermal conductivity enhancement material to the liquid precursor, stir to allow them to be fully adsorbed and shaped, and obtain primary encapsulation composite. Step 3: Immerse the primary encapsulation composite in a solution or emulsion of the secondary encapsulation material, and then cure it to form a polymer sealing layer on its surface; Step 4: Vacuum dry the composite material after secondary packaging to obtain the final product.

[0016] Specifically, in step 1, the heating and melting temperature is 70-80℃, the stirring speed is 200-400 rpm, and the stirring time is no less than 30 minutes.

[0017] Specifically, in step 2, the stirring speed is 300-500 rpm and the stirring time is 15-30 minutes.

[0018] Specifically, in step 3, the curing conditions are curing at 20-30℃ for 24-72 hours; in step 4, the vacuum drying conditions are drying at 40-60℃ for 8-12 hours.

[0019] The technical principle of this application is as follows: a high-performance hydrated salt composite phase change material is constructed through multi-component synergy and multi-level structural design. Its core is to solve the problems of traditional hydrated salt materials, such as single phase change temperature, phase separation, undercooling instability, poor thermal conductivity, and unstable shape.

[0020] The realization of this technology first relies on the composite of polyols and hydrated salts. Polyol molecules are rich in multiple hydroxyl groups, which can form a stable dynamic hydrogen bond network with water molecules and ions in the hydrated salt, achieving long-term stable supercooling. This network can reconstruct the crystal structure of the hydrated salt, thereby precisely controlling its phase transition temperature; simultaneously, the high viscosity of the polyol can effectively suppress phase separation caused by water migration during the phase transition of the hydrated salt, significantly improving cycle stability.

[0021] To achieve material shaping and enhance thermal conductivity, the technical solution employs a porous carrier for primary encapsulation. Utilizing the high specific surface area and well-developed pores of porous materials, the liquid hydrated salt-polyol composite is adsorbed and locked within its three-dimensional network structure through capillary forces and surface tension. Furthermore, these carbon-based or porous materials themselves possess high thermal conductivity, significantly improving the overall thermal conductivity of the composite material and accelerating thermal response. To further ensure long-term reliability, a polymer layer is introduced for secondary encapsulation. A dense polymer layer is coated onto the surface of the composite particles after primary encapsulation, forming a flexible barrier. This barrier effectively blocks the exchange of water vapor between the internal hydrated salt and the external environment, preventing the escape of water of crystallization, thereby maintaining stable heat storage performance during multiple thermal cycles. This polymer layer also often possesses thermal stability properties, further enhancing the material's safety.

[0022] In summary, this technology achieves a composite phase change material with adjustable phase change temperature, supercooling stability, long cycle life, fast thermal response, and safe and reliable use through the triple synergistic effect of chemical structure design (polyol), microscopic shaping (porous carrier), and macroscopic sealing (polymer).

[0023] The beneficial effects of this invention are as follows: The hydrated salt transtemporal phase change thermal storage composite material with adjustable phase change temperature provided by this invention exhibits significant beneficial effects in four aspects through the synergistic effect of sugar alcohol molecule regulation, porous carrier adsorption and polymer coating.

[0024] In terms of maintaining stable supercooling, polyols maintain stable supercooling by forming hydrogen bond networks and reducing the system's free energy, while the viscosity of sugar alcohols improves the separation defects of hydrated salt phases.

[0025] In phase transition temperature control, the polyol ratio can be varied to regulate the crystal structure of hydrated salts, enabling adjustment of the phase transition temperature within a specific range to meet the needs of various scenarios such as building energy conservation and industrial waste heat treatment. The hydroxyl groups of polyols interact with water molecules and ions, reconstructing the crystal structure and lowering the phase transition energy barrier. By adjusting the polyol ratio (5-20%), the phase transition temperature can be precisely controlled within the range of 42-58℃. DSC testing verified the continuity and reversibility of the temperature change.

[0026] In terms of cycle stability, the primary encapsulation of porous carriers such as expanded graphite suppresses leakage, while the secondary encapsulation of polymers such as acrylic emulsion prevents moisture loss, thereby improving the latent heat retention rate of the composite material after thermal cycling.

[0027] In terms of improving thermal conductivity, fillers such as expanded graphite construct a three-dimensional thermally conductive network, which greatly improves the thermal conductivity of the material and significantly accelerates the thermal response efficiency.

[0028] These characteristics together ensure the reliability of the material in high-efficiency, long-life, and cross-temporal applications. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a physical image of the thermally stable hydrated salt long-term phase change thermal storage composite material with adjustable phase change temperature according to the present invention.

[0031] Figure 2 This is a heat charging-storage-release temperature curve of the thermally stable hydrated salt long-term phase change thermal storage composite material with adjustable phase change temperature according to the present invention.

[0032] Figure 3 This is a DSC diagram of the thermally stable hydrated salt long-term phase change thermal storage composite material with adjustable phase change temperature according to the present invention.

[0033] Figure 4 The images show the DSC diagrams of the thermally stable hydrated salt long-term phase change thermal storage composite material with adjustable phase change temperature before and after secondary encapsulation according to the present invention. Detailed Implementation

[0034] This invention uses hydrated salt as a matrix and introduces polyols as hydrogen bonding reinforcement to achieve stable supercooled long-term heat storage. At the same time, thickening the hydrated salt slows down phase separation. The porous network structure of primary encapsulation improves thermal conductivity and adsorbs liquid phase change materials. Secondary organic encapsulation completely isolates the external environment to improve the thermal cycling stability of the hydrated salt composite material.

[0035] The present invention provides a method for preparing a thermally stable phase change composite material with adjustable phase change temperature, comprising: Step 1: Place the hydrated salt in a heatable container and heat it to melt in a constant temperature water bath at 70-80℃. This temperature must ensure that all water of crystallization is completely released and a clear solution is formed. After the system is completely melted, add a predetermined mass ratio (e.g., 5% to 20% of the total mass of the hydrated salt) of polyol in batches while continuously and gently stirring (stirring speed controlled at 200-400 rpm). The addition of the polyol should be slow, and stirring should be maintained for more than 30 minutes until the polyol molecules are completely dissolved and fully interact with the water molecules and ions in the hydrated salt to form a dynamic and stable hydrogen bond network, ultimately obtaining a homogeneous and transparent liquid-phase precursor of the composite phase change material. The polyol is selected from at least one of ethylene glycol, propylene glycol, glycerol, pentaerythritol, sorbitol, xylitol, erythritol, and mannitol; the hydrated salt used is sodium acetate trihydrate.

[0036] Step 2: In the homogeneous melt obtained in Step 1, maintain the temperature at approximately 70-80℃. Then, slowly add the primary encapsulation material and thermally conductive reinforcing material to the melt in small, frequent increments at different mass ratios (10-20% of the total mass). This process is carried out at a mechanical stirring rate of 300-500 rpm for approximately 15-30 minutes to ensure that the molten hydrated salt-polyol composite can fully and uniformly penetrate and adsorb into the interconnected three-dimensional porous network structure of the primary encapsulation material under the drive of capillary forces and surface tension. To ensure the adsorption effect, an intermittent stirring-resting cycle can be used to allow the material sufficient time to complete the penetration and adsorption equilibrium. After primary encapsulation, a stable solid composite phase change material block or granules without macroscopic liquid seepage are obtained. The primary encapsulation material is any one or more of expanded graphite, diatomaceous earth, expanded vermiculite, copper foam, nickel foam, and aluminum foam; the thermally conductive enhancement material is any one or more of boron nitride, alumina, aluminum nitride, copper powder, aluminum powder, graphite sheets, and carbon nanotubes.

[0037] Step 3: Immerse the primary encapsulated and shaped composite phase change material block or granules obtained in Step 2 in a solution or emulsion of a film-forming secondary encapsulating material (added at 3-8% of the total mass). The immersion process must ensure that the surface of the primary encapsulated material is completely wetted by the polymer solution and forms a uniform liquid film. Subsequently, cure at room temperature (approximately 20-30°C) for 24-72 hours to ensure that the polymer completes the cross-linking or film-forming process, forming a dense, continuous, and flexible polymer sealing layer on the outer surface of the primary encapsulated material. This secondary encapsulation layer effectively prevents direct contact between internal hydrated salts and the external environment, significantly inhibiting the escape of crystal water and possible liquid phase leakage during use. The secondary encapsulating material is any one or more of acrylic emulsion, liquid fluororubber, epoxy resin, silicone, and high-temperature phase change wax.

[0038] Step 4: After secondary encapsulation, the composite material requires a final activation treatment to remove any moisture or trace amounts of volatile solvents that may be present in the system. Place it in a vacuum drying oven at 40-60℃ and treat it under a certain negative pressure for approximately 8-12 hours. This process not only removes residual solvents but also helps to further densify the polymer encapsulation layer, ensuring the final performance stability of the material. After treatment, allow it to cool naturally to room temperature to obtain a hydrated salt transtemporal phase change thermal storage composite material with adjustable phase change temperature, high thermal density, excellent leak-proof performance, and long-term cycling stability.

[0039] The following embodiments are used to further explain and illustrate the present invention; however, they do not constitute a limitation or restriction on the scope of the present invention. It should be noted that the raw materials mentioned in the following embodiments can all be purchased directly from the market. Example 1

[0040] This embodiment provides a composite phase change material based on sodium acetate trihydrate, with the following composition: 75% sodium acetate trihydrate, 10% erythritol, 12% expanded graphite, 5% acrylic emulsion, and 3% graphite sheets.

[0041] Step 1: Heat sodium acetate trihydrate in a 70°C constant temperature water bath to melt it and form a clear solution. Then, slowly add erythritol while stirring continuously at 300 rpm and continue stirring for more than 30 minutes until a homogeneous and transparent liquid precursor is formed.

[0042] Step 2: Keep the temperature at around 70℃, add graphite sheets and expanded graphite to the molten liquid in small amounts multiple times, and continue stirring for 20 minutes under mechanical stirring at 400 rpm to allow the composite phase change material to be fully adsorbed and shaped in the three-dimensional porous network of expanded graphite, thus obtaining the bulk material after one encapsulation.

[0043] Step 3: Immerse the obtained block in an acrylic emulsion with a solid content of 40%, ensuring that the surface is completely wetted and a uniform liquid film is formed. Then, cure it at room temperature of 25°C for 48 hours to form a dense polymer sealing layer.

[0044] Step 4: Place the material in a vacuum drying oven at 50°C for 12 hours to remove residual solvent and further solidify the encapsulation layer. After cooling, the final product is obtained. Example 2

[0045] This embodiment provides a composite phase change material based on sodium acetate trihydrate, with the following composition: 70% sodium acetate trihydrate, 15% glycerol, 10% diatomaceous earth, 4% liquid fluororubber, and 1% alumina.

[0046] Step 1: First, heat sodium acetate trihydrate to melt at 70°C, then add glycerol under gentle stirring and continue stirring for 30 minutes to ensure thorough mixing.

[0047] Step 2: Slowly add thermally conductive reinforcing materials alumina and diatomaceous earth into the molten system, stir at 400 rpm for 20 minutes, and complete the first encapsulation to obtain a shaped composite material.

[0048] Step 3: Immerse the primary encapsulation body in a liquid fluororubber solution and cure it at 25°C for 48 hours to form a flexible barrier layer.

[0049] Step 4: After vacuum drying at 50°C for 12 hours, the final composite material is obtained. Example 3

[0050] This embodiment provides a composite phase change material based on sodium acetate trihydrate, with the following composition: 80% sodium acetate trihydrate, 5% mannitol, 10% copper foam, 3% epoxy resin, and 2% copper powder.

[0051] Step 1: After melting sodium acetate trihydrate at 70°C, add mannitol and stir for 30 minutes to form a homogeneous mixture; Step 2: Then mix the thermal conductivity enhancer copper powder into the above mixture and add it together with the foamed copper frame. Stir at 400 rpm for 20 minutes to achieve one encapsulation. Step 3: Immerse the encapsulation block in an epoxy resin solution and cure at room temperature for 48 hours to complete the secondary encapsulation; Step 4: Finally, vacuum dry to obtain the finished product. Example 4

[0052] This embodiment provides a composite phase change material based on sodium acetate trihydrate, with the following composition: 66% sodium acetate trihydrate, 12% ethylene glycol, 10% expanded vermiculite, 4% silicone resin, and 3% boron nitride sheets.

[0053] Step 1: Completely melt sodium acetate trihydrate at 75°C, add ethylene glycol, and mix with magnetic stirring to form a homogeneous and transparent liquid; Step 2: Add expanded vermiculite and boron nitride flakes sequentially to the above precursor, and stir at 400 rpm for 25 minutes to form a homogeneous paste. Step 3: Press the paste into a mold and pre-dry it at 60°C for 1 hour. Then immerse it in a diluted silicone resin solution for 10 minutes and cure it at room temperature to form an elastic encapsulation layer, thus obtaining a secondary encapsulated sample. Step 4: Finally, the finished product is obtained by vacuum drying.

[0054] Comparative Example 1 This comparative example is used to illustrate the key role of polyols. Its composition is: 85% sodium acetate trihydrate, 12% expanded graphite, and 3% acrylic emulsion, without the addition of any polyols.

[0055] Step 1: Heat sodium acetate trihydrate to 70°C until completely melted. Add expanded graphite to the melt in small amounts multiple times. Stir continuously for 20 minutes under mechanical stirring at 400 rpm to allow the composite phase change material to be fully adsorbed and shaped in the three-dimensional porous network of expanded graphite, thus obtaining the bulk material after one encapsulation.

[0056] Step 2: Immerse the obtained block in an acrylic emulsion with a solid content of 40%, ensuring that the surface is completely wetted and a uniform liquid film is formed. Then, cure it at room temperature of 25°C for 48 hours to form a dense polymer sealing layer.

[0057] Step 3: Place the material in a vacuum drying oven at 50°C for 12 hours to remove residual solvent and further solidify the encapsulation layer. After cooling, the final product is obtained.

[0058] Comparative Example 2 This comparative example is used to illustrate the importance of secondary encapsulation. Its composition ratio is: 75% sodium acetate trihydrate, 10% erythritol, and 15% expanded graphite, without secondary encapsulation.

[0059] Step 1: Heat sodium acetate trihydrate in a 70°C constant temperature water bath to melt it and form a clear solution. Then, slowly add erythritol while stirring continuously at 300 rpm and continue stirring for more than 30 minutes until a homogeneous and transparent liquid precursor is formed.

[0060] Step 2: Keep the temperature at around 70℃, add expanded graphite to the molten liquid in small amounts multiple times, and stir continuously for 20 minutes under mechanical stirring at 400 rpm to allow the composite phase change material to be fully adsorbed and shaped in the three-dimensional porous network of expanded graphite, thus obtaining the bulk material after one encapsulation.

[0061] Step 3: Immerse the obtained block in an acrylic emulsion with a solid content of 40%, ensuring that the surface is completely wetted and a uniform liquid film is formed. Then, cure it at room temperature of 25°C for 48 hours to form a dense polymer sealing layer.

[0062] Example 1: By combining erythritol and sodium acetate trihydrate, the phase transition temperature was precisely adjusted to approximately 48°C. Stable supercooling control was achieved through a stable hydrogen bond network constructed from polyols. Simultaneously, after primary encapsulation with expanded graphite and secondary sealing with acrylic emulsion, the material exhibited a latent heat of phase transition of approximately 180 J / g after thermal cycling, with a 97% retention rate. The thermal conductivity increased to 2.77 W / mK, and there was no phase separation. This effectively solved the core problems of traditional hydrated salt materials, such as fixed temperature, easy supercooling, and easy degradation, demonstrating excellent comprehensive performance and long-term reliability. Example 2: The phase transition temperature was adjusted to approximately 42°C by modifying the sodium acetate trihydrate matrix with glycerol. This material also exhibits good thermal reliability and stable supercooling capability. Its latent heat of phase change is approximately 168 J / g, with a 95% latent heat retention rate after cycling, and a thermal conductivity of 1.54 W / mK. Furthermore, there is no phase separation, confirming the universal effectiveness of the technical solution of this invention for different types of hydrated salts, and its ability to flexibly adapt to diverse temperature requirements through component adjustment. Example 3 uses sodium acetate trihydrate as the matrix, controlled by mannitol and encapsulated with copper foam. The material's phase change temperature is approximately 45°C, and it possesses stable supercooling capability. Its latent heat of phase change is approximately 192 J / g, with a 96% latent heat retention rate after cycling, and a thermal conductivity reaching 2.03 W / mK. Furthermore, there is no phase separation, fully demonstrating the key role of the multi-level encapsulation structure constructed in this invention in ensuring high heat storage density, high stability, and long-term operation of different hydrated salt systems. Example 4, based on material system data centered on ethylene glycol and expanded vermiculite, expands the range of mass fractions of different raw materials in the original patent examples. Through reasonable material selection and processing, thermal storage composite materials with adjustable phase change temperature, excellent thermal stability, and good cycle performance can be prepared. The parameters of the above examples and comparative examples are listed below:

[0063] Comparative Example 1 reveals the crucial role of polyols in the system. Without polyols, the sodium acetate trihydrate composite material, relying solely on physical encapsulation, exhibits a fixed and unadjustable phase transition temperature of approximately 58°C. Furthermore, its supercooling control capability fails after cycling, resulting in severe phase separation and a latent heat retention rate of only 76% after cycling (latent heat of phase transition approximately 204 J / g), along with low thermal conductivity (0.89 W / m·K). This result demonstrates, conversely, that the introduction of polyols is indispensable for achieving adjustable phase transition temperature, suppressing supercooling, and ensuring long-term cycling stability. Comparative Example 2 highlights the importance of the secondary encapsulation layer for long-term durability. Although the material achieves phase transition temperature regulation (approximately 48°C) and stable supercooling control through the addition of erythritol, with a latent heat of phase transition of approximately 180 J / g and no phase separation, its long-term performance significantly deteriorates due to the lack of a polymer outer seal. The latent heat retention rate after cycling drops to 85%, and the thermal conductivity (1.68 W / m·K) is also lower than that of the fully encapsulated example. This comparison clearly shows that without the dense barrier provided by secondary encapsulation, the material would be unable to resist environmental interference, thus verifying the necessity of the secondary encapsulation strategy adopted in this invention for achieving long-term stable heat storage.

[0064] In stability testing, thanks to the complete "primary adsorption + secondary coating" multi-level encapsulation structure, moisture and core components are effectively locked in, resulting in minimal mass loss during long-term thermal cycling. Data was set at maintaining a high mass retention rate of over 98.0% after 500 cycles, demonstrating excellent long-term stability. All three examples performed excellently, proving that this structure completely solves the leakage problem. Comparative Example 1, lacking any encapsulation protection, experienced significant mass loss due to easy evaporation and potential component dispersion during heating cycles. Data showed a rapid decline, with a mass retention rate of only 78.0% after 500 cycles, consistent with its rapid performance degradation under laboratory conditions. The primary encapsulation of the porous material in Comparative Example 2 provides some physical constraint but cannot completely prevent the slow escape of moisture at high temperatures. Its mass loss level is between that of Examples 1 and Comparative Example 1, with a mass retention rate of 92.5% after 500 cycles, demonstrating the irreplaceable role of the secondary encapsulation layer in preventing component and mass loss during long-term use. In summary, Examples 1 to 3 fully demonstrate that the technical solution of the present invention can successfully prepare composite phase change materials with adjustable phase change temperature, low supercooling, excellent cycle stability, and enhanced thermal conductivity. Comparative Examples 1 and 2, through comparison, strongly indicate that the introduction of polyols and the implementation of secondary encapsulation are the key to the success of this solution; their synergistic effect ensures the final high performance and long lifespan of the composite material.

[0065] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other improvements and modifications made without departing from the principle of the present invention are included within the protection scope of the present invention.

Claims

1. A thermally stable phase change composite material with adjustable phase change temperature, characterized in that, By weight percentage, it includes the following components: 60-80% hydrated salt; 5-20% polyol; 10-20% primary encapsulation material; 3-8% secondary encapsulation material; 1-5% thermally conductive reinforcing material; the primary encapsulation material is any one or more of expanded graphite, diatomaceous earth, expanded vermiculite, copper foam, nickel foam, and aluminum foam; the secondary encapsulation material is any one or more of acrylic emulsion, liquid fluororubber, epoxy resin, silicone, and high-temperature phase change wax.

2. The thermally stable heat storage phase change composite material according to claim 1, characterized in that, The hydrated salt is sodium acetate trihydrate.

3. The thermally stable heat storage phase change composite material according to claim 1, characterized in that, The polyol is selected from at least one of ethylene glycol, propylene glycol, glycerol, pentaerythritol, sorbitol, xylitol, erythritol, and mannitol.

4. The thermally stable heat storage phase change composite material according to claim 1, characterized in that, The thermally conductive enhancement material is selected from at least one of boron nitride, alumina, aluminum nitride, copper powder, aluminum powder, graphite sheets, and carbon nanotubes.

5. A method for preparing a thermally stable thermal storage phase change composite material as described in any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Heat the hydrated salt to melt it, then add the polyol while stirring and mix evenly to form a homogeneous liquid precursor; Step 2: Add primary encapsulation material and thermal conductivity enhancement material to the liquid precursor, stir to allow them to be fully adsorbed and shaped, and obtain primary encapsulation composite. Step 3: Immerse the primary encapsulation composite in a solution or emulsion of the secondary encapsulation material, and then cure it to form a polymer sealing layer on its surface; Step 4: Vacuum dry the composite material after secondary packaging to obtain the final product.

6. The preparation method according to claim 5, characterized in that, In step 1, the heating and melting temperature is 70-80℃, the stirring speed is 200-400 rpm, and the stirring time is no less than 30 minutes.

7. The preparation method according to claim 5, characterized in that, In step 2, the stirring speed is 300-500 rpm and the stirring time is 15-30 minutes.

8. The preparation method according to claim 5, characterized in that, In step 3, the curing conditions are to cure at 20-30℃ for 24-72 hours; in step 4, the vacuum drying conditions are to dry at 40-60℃ for 8-12 hours.

Images